Avermectin compounds are natural products produced by the fermentation of Streptomyces avermitilis as disclosed in U.S. Pat. No. 4,310,519 to Albers-Schonberg et al. The avermectin compounds have a natural .alpha.-L-oleandrosyl-.alpha.-L-oleandrosyloxy group at the 13-position. In U.S. Pat. No. 4,203,976 to Fischer et al certain synthetic procedures are disclosed for glycosylting various hydroxy groups or the avermectin molecule, including the 4"-hydroxy of the avermectin disaccharide group. The culture Saccharopolyspora erythrea identified in the culture collection of Merck & Co., Inc. as MA 1625 is a known culture, publicly available from the American Type Culture Collection at 12301 Parklawn Drive, Rockville, MD 20852, under the accession number ATCC 11635, and further described in Corcoran, Methods in Enzymology 43 pg 487-498 (1975).